1=======================
2S3C24XX Suspend Support
3=======================
4
5
6Introduction
7------------
8
9  The S3C24XX supports a low-power suspend mode, where the SDRAM is kept
10  in Self-Refresh mode, and all but the essential peripheral blocks are
11  powered down. For more information on how this works, please look
12  at the relevant CPU datasheet from Samsung.
13
14
15Requirements
16------------
17
18  1) A bootloader that can support the necessary resume operation
19
20  2) Support for at least 1 source for resume
21
22  3) CONFIG_PM enabled in the kernel
23
24  4) Any peripherals that are going to be powered down at the same
25     time require suspend/resume support.
26
27
28Resuming
29--------
30
31  The S3C2410 user manual defines the process of sending the CPU to
32  sleep and how it resumes. The default behaviour of the Linux code
33  is to set the GSTATUS3 register to the physical address of the
34  code to resume Linux operation.
35
36  GSTATUS4 is currently left alone by the sleep code, and is free to
37  use for any other purposes (for example, the EB2410ITX uses this to
38  save memory configuration in).
39
40
41Machine Support
42---------------
43
44  The machine specific functions must call the s3c_pm_init() function
45  to say that its bootloader is capable of resuming. This can be as
46  simple as adding the following to the machine's definition:
47
48  INITMACHINE(s3c_pm_init)
49
50  A board can do its own setup before calling s3c_pm_init, if it
51  needs to setup anything else for power management support.
52
53  There is currently no support for over-riding the default method of
54  saving the resume address, if your board requires it, then contact
55  the maintainer and discuss what is required.
56
57  Note, the original method of adding an late_initcall() is wrong,
58  and will end up initialising all compiled machines' pm init!
59
60  The following is an example of code used for testing wakeup from
61  an falling edge on IRQ_EINT0::
62
63
64    static irqreturn_t button_irq(int irq, void *pw)
65    {
66	return IRQ_HANDLED;
67    }
68
69    statuc void __init machine_init(void)
70    {
71	...
72
73	request_irq(IRQ_EINT0, button_irq, IRQF_TRIGGER_FALLING,
74		   "button-irq-eint0", NULL);
75
76	enable_irq_wake(IRQ_EINT0);
77
78	s3c_pm_init();
79    }
80
81
82Debugging
83---------
84
85  There are several important things to remember when using PM suspend:
86
87  1) The uart drivers will disable the clocks to the UART blocks when
88     suspending, which means that use of printascii() or similar direct
89     access to the UARTs will cause the debug to stop.
90
91  2) While the pm code itself will attempt to re-enable the UART clocks,
92     care should be taken that any external clock sources that the UARTs
93     rely on are still enabled at that point.
94
95  3) If any debugging is placed in the resume path, then it must have the
96     relevant clocks and peripherals setup before use (ie, bootloader).
97
98     For example, if you transmit a character from the UART, the baud
99     rate and uart controls must be setup beforehand.
100
101
102Configuration
103-------------
104
105  The S3C2410 specific configuration in `System Type` defines various
106  aspects of how the S3C2410 suspend and resume support is configured
107
108  `S3C2410 PM Suspend debug`
109
110    This option prints messages to the serial console before and after
111    the actual suspend, giving detailed information on what is
112    happening
113
114
115  `S3C2410 PM Suspend Memory CRC`
116
117    Allows the entire memory to be checksummed before and after the
118    suspend to see if there has been any corruption of the contents.
119
120    Note, the time to calculate the CRC is dependent on the CPU speed
121    and the size of memory. For an 64Mbyte RAM area on an 200MHz
122    S3C2410, this can take approximately 4 seconds to complete.
123
124    This support requires the CRC32 function to be enabled.
125
126
127  `S3C2410 PM Suspend CRC Chunksize (KiB)`
128
129    Defines the size of memory each CRC chunk covers. A smaller value
130    will mean that the CRC data block will take more memory, but will
131    identify any faults with better precision
132
133
134Document Author
135---------------
136
137Ben Dooks, Copyright 2004 Simtec Electronics
138